For example, as described in Japanese Unexamined Patent Application Publication No. 2004-161123, a rearview outer mirror provided at a lateral part of an automobile contains a mirror surface angle adjusting device for tiltably holding a mirror.
As shown in FIG. 13, the mirror surface angle adjusting device described in Japanese Unexamined Patent Application Publication No. 2004-161123 is attached to a back side of a mirror M (i.e., a vehicle's front side), and it includes a pivot plate Hc for holding the mirror M through a mirror holder Mh, and an actuator Ac for tiltably holding this pivot plate Hc.
The actuator Ac includes an annular receiving part P of which inner face is molded to a circular shape, and rods Q for pushing or pulling the pivot plate Hc. Although being not shown, the actuator Ac is equipped therein with one or more motors for applying driving power to the rods Q, and both a worm wheel and a worm for transmitting the driving force of the motor to the rods Q.
In addition, as shown in FIG. 14, the pivot plate Hc is provided, at its rear face, with an annular sliding portion P′ slidably held by the receiving part P, and a pair of engaging portions Q′ mating with tips of the respective rods Q.
Furthermore, when the rods Q move back or forth by controlling the rotational direction and rotational amount of the motor, the pivot plate Hc is tilted with respect to the actuator Ac.
Actually, as shown in FIG. 14, the worm wheel S contained in the actuator Ac is held by being sandwiched between a first housing R1 and a second housing R2 which both constitute a casing of the actuator Ac.
However, in such a structure for holding the worm wheel S, if any assembly error between the first housing R1 and the second housing R2 occurs, the assembly accuracy of the worm wheel S may be affected. For example, if a contact pressure between the worm wheel S and both the housings R1 and R2 excessively increases due to the assembly error between the housings R1 and R2, abnormal noises may be sounded in response to a rotational movement of the worm wheel S, and furthermore, a smooth rotational movement of the worm wheel S may be hindered. Moreover, if an excess gap is formed between the worm wheel S and both the housings R1 and R2 due to the assembly error between the housings R1 and R2, “deviation” occurs in a central axis (i.e., a rotation axis) of the worm wheel S, which may inhibit its smooth rotational movement.
Moreover, in the above-described holding structure for the worm wheel S, the worm wheel S is not secured until the first housing R1 and the second housing R2 are assembled. Therefore, during the manufacture of the actuator Ac, a worker must assemble the first housing R1 and the second housing R2 while being careful not to cause a deviation in the position (i.e., the central axis) of the worm wheel S.
As described above, in conventional mirror surface angle adjusting devices in which the worm wheel S is sandwiched between the first and second housings R1 and R2, the assembly error between the first housing R1 and the second housing R2 has a great influence upon the assembly accuracy of the worm wheel S. Furthermore, the assembly process thereof cannot be done simply and promptly.